A book for inquisitive children

 kw: book reviews, nonfiction, science, questions answered, compendia

We all know a youngster who asks "Why?" about almost everything. Sometimes they're just challenging a parent's decision, but other times the question is, "Why is the sky blue?", or, "Why do knuckles crack?"

Jay Ingram likes to answer questions…in detail. In Why Do Onions Make Me Cry: Answers to Everyday Science Questions You've Always Wanted to Ask (a follow-on to The Book of Why), he tackles 51 such questions, with answers ranging from two to five pages, plus each of the five sections of the book has a "History Mystery" such as "Did Newton really get hit on the head by an apple, inspiring his thoughts on gravity?" The length of the answers and their comprehensiveness indicate that Mr. Ingram knows you'll get follow-on Why's.

Some questions lead to others, sometime in interesting directions. In his answer to "Why is the sky blue?", he also digs into how the words for colors seem to have developed over time. "Blue" wasn't much of a concept long ago, possibly because other than the sky, not much is blue (flax flowers and certain butterflies, and that's about it), while purple was well known because purple dye is made from chemicals obtained from certain sea snails. Thus, blue things were called "purple" until truly blue dyes, such as woad, became economical to produce, while words for red, yellow and green arose very early. Color perception probably didn't change, but people's ideas about colors changed.

While we're in the blue sky area, look closely at this satellite photo. The bluish tint in the upper right area is from looking through the blue sky from above! The higher mountains don't have nearly so much air above them, and the color doesn't show.

This leads me to a question about blue skies that this book doesn't answer, and I'll dig into it as a bonus: 

Does every planet with an atmosphere have a blue sky?

The easy answer is No, because we have all seen recent pictures from Mars and the sky is pinkish. But there is an underlying complication. Mars has such a thin atmosphere that Rayleigh scattering, which makes the sky so blue on Earth, is a very, very small effect. The pinkish dust that is nearly always present in the air on Mars overwhelms the scattered blue light. On rare occasions, the wind on Mars calms enough for dust to settle, and the sky gets almost black, with just a bit of very deep blue. So let's refine the question: Does every planet have a blue sky when the air is very clear?

This gets into the colors of stars! We call the Sun a yellow star because we see it through our atmosphere, and 1/3 of its light is scattered by the air to make all that blueness. The light that gets straight to us is thus a pale yellow. From the International Space Station or any other orbiting craft, the Sun appears utterly white. This makes sense. Our eyes evolved to see "average daylight" as "white", and the color of the light that reaches a colorless object on Earth is direct sunlight plus blue light from the rest of the sky, and that adds back to the pale yellow to be white.

You might have heard or read about bluish and reddish stars. Most of the stars we see at night are a bit bluish compared to the Sun. The visible ones are bright, hot stars, and stars hotter than the Sun are bluer. A few stars, such as Betelgeuse in Orion and Antares in Scorpio, look reddish if you look carefully. Looking at one of these stars with slightly out-of-focus binoculars lets you see the rather orange color more clearly. They are redder than the Sun because they aren't as hot. However, they are still hotter than the filament in an incandescent light bulb, which actually emits a rather orange-colored light. Our color vision adapts to this and it looks "white enough" to us, unless we look at a lamp next to a well-lit window.

Suppose there is a planet orbiting one of those orange-colored stars. Would it have a blue sky? There are two answers to this. Firstly, to us, the star would look slightly more orange than the Sun does, and the sky, if very clear, would be "less orange", and probably would look pale blue. But Secondly, if there are creatures on that planet which evolved there, they to them their star looks white, and the sky would look blue! On a hotter star such as Sirius, which is already bluish, the sky above any planet would be a more intense blue than our sky, barring pink dust, of course.

Enjoy this book, and if you have kids that are full of questions, keep a copy on hand, so you'll have at least 50 questions that you can actually answer.